1. Field of the Invention
This invention relates to ultrasonic horns for ultrasonic bonding of materials such as composite multiple-layer webs, and in particular, a method and system for directly measuring and controlling the amplitude of an ultrasonic horn during processing of the material being bonded.
2. Description of Prior Art
Ultrasonic bonders are known in the art. See, for example, U.S. Pat. No. 4,713,132 to Abel et al. which teaches a method and apparatus for ultrasonic bonding of a moving web, and U.S. Pat. No. 5,591,298 to Goodman et al. which teaches a machine for ultrasonic bonding utilizing a stationary ultrasonic horn. Stationary ultrasonic horn bonders are limited to operating on webs traveling at low speeds, in part, because, at higher web speeds, the web being bonded tends to pile up, or bunch up, at the leading edge of the stationary ultrasonic horn. In addition, the amplitude of a stationary ultrasonic horn during normal production of ultrasonically bonded materials is normally controllable only indirectly. Certain problems associated with material handling by stationary ultrasonic horn bonding equipment are addressed by U.S. Pat. No. 5,817,199 to Brennecke et al. which teaches the use of a rotating ultrasonic horn in combination with an anvil roll to ultrasonically bond web materials together. However, no method for directly controlling the amplitude of either a stationary or rotating ultrasonic horn during ultrasonic bonding of the web material is taught or suggested by the prior art known to me.
The use of light as a means for measuring the physical attributes of various types of objects is well known to those skilled in the art. For example, U.S. Pat. No. 4,046,477 to Kaule teaches an interferometric method and apparatus for sensing surface deformation of a workpiece subjected to acoustic energy in which the surface of the workpiece is illuminated by a laser beam which is reflected therefrom and passed through an optical beam splitter to produce a measuring beam portion and a reference beam portion. The measuring beam portion after reflection at a mirror is transmitted to photoelectric means while the reference beam portion is time delayed by means of an optical delay path and then brought to interfere with the measuring beam portion at the photoelectric means.
U.S. Pat. No. 3,918,816 to Foster et al. teaches a method and apparatus for dimensional inspection of a tire involving mounting of the tire for rotation and impinging on its tread surface a laser beam, analyzing the backscattered radiation to determine the position in space of the point of impingement, and selectably scanning or positioning the laser to measure various positions on the tire surface.
U.S. Pat. No. 4,086,808 to Camac et al. teaches a method and apparatus for measuring and monitoring vibrational or similar motion in mechanical elements in which retroreflectors on the elements are illuminated with monochromatic light, such as a laser, and the reflected beams form an interference pattern. Shifts in the interference fringes correspond to motion which changes the relative length of the paths of reflected light, and these shifts are counted or analyzed to monitor such motion.
U.S. Pat. No. 4,659,224 to Monchalin teaches the use of a laser beam and an interferometer of the confocal Fabry-Perot type for non-contact reception of ultrasonic waves wherein the interferometer detects the frequency shift caused by the Doppler effect in an incident layer beam as a result of ultrasonic deformations of a workpiece.
U.S. Pat. No. 4,619,529 to Iuchi et al. teaches an interferometric contact-free measuring method for sensing, by a laser beam, motional surface deformation of a workpiece subject to an ultrasonic vibration in which the laser beam is split into a measuring beam incident upon a measuring point on the workpiece and a reference beam incident upon a reference point close to the measuring point, and the two beams, after reflection, are brought into a common optical detector.